Flexor Pollicis Brevis Under the Skin, Palmar View

Description

Palmar soft tissues are reflected to highlight the flexor pollicis brevis within the thenar eminence of an adult male hand. Its superficial head lies anterior to the first metacarpal and trapezium region, while the deeper head sits closer to the first metacarpal shaft and adductor pollicis, the two converging toward the radial sesamoid at the metacarpophalangeal joint of the thumb. Medially, the adductor pollicis mass defines the ulnar border of the first web space, and laterally the abductor pollicis brevis forms the most superficial radial contour of the thenar pad; the flexor pollicis longus tendon tracks deep to these thenar muscles en route to the distal phalanx. Bones of the carpus, metacarpals, and phalanges provide fixed landmarks. Orientation is unmistakably palmar. Thumb opposition depends on coordinated thenar function, and flexor pollicis brevis is the short flexor that couples metacarpophalangeal flexion with the rotational component driven by opponens pollicis at the first carpometacarpal joint. Denervation patterns matter here: the superficial head commonly receives the recurrent branch of the median nerve, while the deep head often has ulnar nerve input, a split that explains partial thenar weakness in some carpal tunnel syndrome presentations. Small structure, big consequences. This view also helps when teaching why thenar atrophy spares sensation in isolated recurrent branch injury, or when planning an approach for thumb MCP procedures where the radial sesamoid and volar plate sit immediately distal to the muscle insertion. Use this plate in gross anatomy labs, hand therapy curricula, and surgical education modules on thenar anatomy, carpal tunnel release, and basal thumb mechanics, and in medical publishing where precise thenar topography and nomenclature are required for captions and callouts. Anatomical accuracy verified by SciePro's Medical Advisory Board.